1. Field of the Invention
The present invention relates to a method and apparatus for cutting into and drilling through materials in general. More specifically, the present invention relates to a method and apparatus for cutting into and drilling through materials using the liquid, gaseous and/or supercritical phase of a fluid along with certain solid abrasive materials.
2. Prior Art
Jet assisted drilling for drilling horizontal holes, primarily for oil and gas wells, has been attempted since at least the 1960s, but required high-pressure to increase penetration rates. High-pressure fluid jet-assisted drilling has also been studied, such as using water jets positioned close to the cutting teeth of conventional bits to improve their penetration rate. While effective, the high-pressure fluid jet-assisted drilling technique still requires a means to transmit both force and high pressure fluid to the drilling bit, and thereby makes the supporting drill rod stiffer and more difficult to turn. In addition, each of the hundreds of tool joints that are assembled into the drilling string of pipe must be fully sealed against one another, as the pipe is assembled, in order to effectively deliver the high pressure fluid to the bit while concurrently delivering sufficient torque and stiffness to the bit as to drive it forward into the rock.
To improve the performance of a drilling jet stream, certain small abrasive particles have been introduced into the drilling fluid (mainly water based). By so doing, and configuring the system so that there is an energy transfer between the pressurized fluid and the particles, the particles can be given sufficient kinetic energy that they will cut into the target material ahead of the drill bit. Energy transfer from the water to the particles is, however, inefficient, so that the particles gain only a fraction of the velocity that the liquid jet would have without them. The combination of high velocity solid particles in liquid allows the potential for drilling through the hardest material, provided that the supply pressure to the water is high enough to overcome the low energy transfer efficiency, and that the kinetic energy imparted to the abrasive particles exceeds that required to break the targeted material. Currently, several abrasive water jet systems have been developed based on this method. The requirement of a very high water pressure to cut some rock targets is problematic, especially when the drill is attached to the end of a coiled-tube system, since the thin wall of such a pipe can only safely carry a certain pressure and still perform its function.
One of the important components in the abrasive water jet system is the cutting nozzle. The cutting nozzle designs that have been used for conventional high-pressure water jet drilling are designed typically with a converging conic section of around 12-20 degrees leading into a narrow bore (on the order of 0.04 inches diameter) of short length (nominally around 4-10 times bore diameter), as shown in FIG. 1. The design intends to accelerate the water jet stream to a maximum velocity before being directed at the target material.
When high-pressure jets are used in other applications, it is on occasion advantageous that the water jet be dispersed to cover a larger area. There are a number of different ways in which the flow of fluid from a nozzle orifice can be disrupted, so that it covers a larger area. One method to broaden the resulting exit stream of the water jet is to place turning vanes in the section of the nozzle immediately upstream of the section where the diameter narrows. If this is done, and water injected through it, then the swirling action of the water jet stream can induce cavitation in the central section of the resulting water jet stream, with the collapse of the cavitation cloud enhancing cutting performance, but still at a relatively slow penetration rate. This work has been described by Johnson and Conn of Hydronautics and described in U.S. Pat. Nos. 3,528,704 and 3,713.699. A similar use of turning vanes, placed immediately upstream of the nozzle, has been used by companies such as Steinen and Spraying Systems, wherein the resulting water jet is allowed to egress into the atmosphere where it spreads to cover a large circular area, which has benefits in cleaning such surfaces as it might be directed against. The latter systems do not have sufficient power, as normally applied, to be able to cut into rock and similar target material.
A concern with the performance of an abrasive water jet stream for drilling comes from the interference to free passage that occurs in the interaction of particles and water entering the cutting zone at the target, with the spent fluid, abrasive and removed rock leaving that zone. This is compounded when the jet is very narrow and cutting a very thin slit into the target surface. Efficiencies of cutting are also constrained by a need to ensure that all the rock (or other target materials and debris) ahead of the drill has been removed over the full diameter of the face of the drilling tool, by directing a jet or jets to impact that full area, before the nozzle advances further into the rock (or other target). Without that full removal of material over the full face, the nozzle cannot advance past that remaining obstruction. Concurrently, in developing a design for a light, portable and simple drill, the need for a rotation system to ensure that abrasive jets fully sweeps the area ahead of the nozzle and drill assembly to remove any impeding rock, adds considerable complexity, cost and weight to the unit.
Currently, jet assisted drilling using supercritical fluid or dense gas, such as carbon dioxide, as a drilling fluid has been investigated, such as with the coiled tubing drilling method and apparatus described in U.S. Pat. No. 6,347,675 to Kollé. The method in U.S. Pat. No. 6,347,675 uses either a supercritical fluid or a dense gas (such as carbon dioxide, methane, natural gas, or a mixture of those materials) as a drilling fluid. To maintain the drilling fluid in its supercritical phase, the method requires the pressure to exceed 5 MPa (preferably, to exceed 7.4 MPa with CO2), which can be achieved only by employing heavy walled drill pipe and special connections. Also, a surface choke manifold at the drill site is required to control the resultant return flow. Alternately, the drilling process can be controlled by “capping” the well with drilling mud. This process uses additives in the drilling fluid to increase the density of that fluid, which fills the annulus between the drilling tube and the surrounding rock wall. This passage is the return path, through which the cuttings must pass to reach the surface and clear the hole. By increasing the down-hole pressure around the drilling bit, however, a higher driving pressure is required to effectively cut into the rock target, that may well be in the range from 50 to 200 MPa and this exceeds the pressure capability of most coiled tubing. Also, the presence of this higher density fluid provides a more resistive barrier to the jet motion. In passing through this barrier the performance of the jet is degraded, and a poor cutting ability in penetrating the target rock results.
Potter et al. (U.S. Pat. No. 5,771,984) discloses spallation or thermal processes for weakening the rock by heat. The gases and fluids injected are for combustion to form hot fluids to perform the disclosed process without adding solids to the injected stream. All return flow is specifically within and up the drill pipe. In contrast, the present invention disclosed herein uses erosive cutting or abrasive cutting by use of a slurry wherein solids are suspended in the liquid (which is normally gas in a liquid state). Additionally, return flow can travel up to the surface outside of the drill pipe.
Bingham et al. (U.S. Pat. No. 5,733,174) provides a system using supercritical or liquified gases as the carrier fluid. Solids are the supercritical gas in a solid form. The solids are neither hard nor dense resulting in inefficient cutting. In contrast to the present invention, Bingham et al. does not flash the supercritical carrier liquid into a gas either inside or just outside the nozzle. Bingham requires a central slurry jet of supercritical liquid and supercritical solid and an outer sheet of supercritical liquid and an outer gas.
Therefore, there remains a need to provide a set of new and improved jet-assisted drilling and/or cutting method and apparatus that performs targeted drilling or cutting, with high efficiency, increased speed, easy advancing of the device, and ready removal of drilling/cutting debris, and lower pressure operation.